Work through each stage in order. The next step unlocks only after you confirm the current one is complete.
Not yet safe to isolate — work through each stage above in order, starting with identifying the circuit.
Safe isolation is the process of disconnecting a circuit from its supply and proving it dead before any work begins. Failure to follow the correct sequence is one of the most common causes of electrical fatalities in the UK.
The sequence matters. Proving the test instrument works on a known live source before testing the circuit (step 3) and again afterwards (step 7) is not optional — a faulty test instrument will give a false dead reading on a circuit that is actually still live. This two-stage check is what separates a genuine safe isolation from simply pointing a meter at the terminals, and it's the specific requirement HSE Guidance Note GS38 places on anyone using test equipment to prove a circuit dead.
For three-phase supplies, all three phases and the neutral must be proved dead individually — six readings in total (phase-to-phase and phase-to-neutral), plus each phase to earth. A circuit that reads dead on one phase may still be live on another, so never assume a reading on L1 applies to L2 or L3.
If any voltage reading during the test-for-voltage step is not zero, the circuit is still live. Stop immediately and do not touch any part of it. This checklist requires that to be acknowledged explicitly before it allows a reset — investigate and resolve the fault using your normal safe working procedures before attempting isolation again.
This procedure follows HSE Guidance Note GS38 (electrical test equipment for use by electricians), which requires proving a test instrument before and after use and proving all phases and the neutral dead, and the Electricity at Work Regulations 1989. Isolation and locking-off requirements also reflect Section 537 of BS 7671:2018+A2:2022 (18th Edition Amendment 2). This page is a procedural guide only, not a substitute for your employer's safe working procedures or current HSE guidance.